Multi-channel MPEG between headend and fiber node

ABSTRACT

A system and related methodology are provided that are configured to receive, at a first network element, multiple channels of video delivered as respective streams of packets, form a packet switched communication frame including a sub-layer header, encapsulate packets from the multiple channels of video into a payload field of the communication frame to obtain encapsulated packets, identify the encapsulated packets in the payload field with respective tags in the sub-layer header, designate the encapsulated packets in the payload field with respective launch values in the sub-layer header, and transmit the communication frame to a second network element. The first network element may be a universal edge quadrature amplitude modulator (UEQAM) and the second network element may be a relatively distant fiber node of a cable plant. The sub-layer header may also include Program Clock Reference (PCR) offset data that can be used for PCR re-stamping.

TECHNICAL FIELD

The present disclosure relates to processing data in an electronic network.

BACKGROUND

Cable operators have deployed high-speed data services on cable television systems including, among other services, Internet service and high speed video service. Internet service may be supported by a cable modem that allows a computer to communicate over an ordinary cable TV network Hybrid Fiber Coax (HFC) physical plant. A Cable Modem Termination System (CMTS) connects the cable TV network to a data network, such as the Internet. The Data-Over-Cable Service Interface Specification (DOCSIS) is one of the cable modem standards used for transferring data over the cable TV network. Video service may be provided over the same physical plant, but instead of the cable plant being connected to a cable modem in the customer premises, the cable plant is instead coupled to a set-top-box that supplies a video signal to, e.g., a television set.

Increasing demand for cable data services requires additional CMTS processing capacity and features. This can be prohibitively expensive since each CMTS provides routing, DOCSIS Media Access Control (MAC) processing, downstream signal modulation and upstream signal demodulation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example topology in which multi channel MPEG (MCM) DOCSIS External Physical (PHY) Interface (DEPI) logic is employed to deliver/exchange DOCSIS data between a Universal Edge Quadrature Amplitude Modulator (QAM) (UEQAM) and a Downstream Physical (DS-PHY) Module.

FIGS. 2A and 2B are example block diagrams of a Line Card of a UEQAM and the DS-PHY Module that support DEPI MCM.

FIG. 3 is an example block diagram of aspects of the DS-PHY Module that supports DEPI MCM, including QAM processing.

FIG. 4 shows a DEPI MCM data-plane packet format in accordance with one possible implementation.

FIG. 5 shows an MCM Sub-Layer header and payload that is part of the DEPI MCM data-plane packet.

FIGS. 6 and 7 depict example flowcharts illustrating operations for effecting multi-channel MPEG DEPI between a UEQAM and a DS-PHY Module in accordance with one possible implementation.

FIG. 8 shows a block diagram of a topology in which an MPEG multiplexer is implemented as a primary MPEG multiplexer and a secondary MPEG multiplexer disposed, respectively, in a headend/UEQAM/CMTS and a DS PHY Module/fiber node of the cable plant in accordance with one possible implementation.

FIGS. 9A and 9B together show an MCM/Multi Channel Launch (MCL) Sub-Layer header and payload that is part of a DEPI MCM/MCL data-plane packet in accordance with one possible implementation.

FIGS. 10 and 11 depict example flowcharts illustrating operations for effecting MPEG MCL between the primary MPEG multiplexer and the secondary MPEG multiplexer in accordance with one possible implementation.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

Described herein are a system and related methodology that are configured to receive, at a first network element, multiple channels of video delivered as respective streams of packets, form a packet switched communication frame including a sub-layer header, encapsulate packets from the multiple channels of video into a payload field of the communication frame to obtain encapsulated packets, identify the encapsulated packets in the payload field with respective tags in the sub-layer header, designate the encapsulated packets in the payload field with respective launch values in the sub-layer header, and transmit the communication frame to a second network element. The first network element may be a universal edge quadrature amplitude modulator (UEQAM) and the second network element may be a relatively distant fiber node of a cable plant. The sub-layer header may also include Program Clock Reference (PCR) offset data that can be used for PCR re-stamping.

At the second network element, e.g., a fiber node, the methodology includes receiving the communication frame including a payload and a sub-layer header, recovering video packets from the payload of the communication frame, selecting stream processing resources based on information in respective tags in the sub-layer header, wherein the tags correspond with respective video packets, processing the video packets using the selected stream processing resources; and determining a time for launching respective video packets based on launch values received on a per-packet basis in the sub-layer header. PCR re-stamping may be performed based on the PCR offset data.

In one possible implementation, the sub-layer header is part of or embodied in a Layer 2 Tunneling Protocol Version 3 (L2TPv3) transport mechanism.

Example Embodiments

FIG. 1 is a block diagram of an example topology in which multi channel MPEG (MCM) DOCSIS External Physical (PHY) Interface (DEPI) logic is employed to deliver/exchange DOCSIS frames between a first network element such as a Universal Edge Quadrature Amplitude Modulator (QAM) (UEQAM) and a second network element such as a Downstream Physical (DS-PHY) Module. As shown, a DOCSIS MAC 120 is in communication with a wide area network 130, which may be, e.g., the Internet. The DOCSIS MAC 120 may include a processor 125 that has access to memory 127. Also in communication with DOCSIS MAC 120 is a Line Card 122 that enables downstream connectivity with Universal Edge QAM (UEQAM) 150 via a packet switched network 135. That is, Line Card 122 functions as an interface to a network (e.g., a DOCSIS Converged Interconnect Network (CIN)). Line Card 122 could be a separate component or integrated within the DOCSIS MAC 120.

Although shown as separate components, DOCSIS MAC 120 and Line Card 122, along with processor 125 and memory 127, could be configured together in a single component or arranged, separately, in some other configuration that still enables the functionality described herein.

UEQAM 150 similarly comprises a processor 125, memory 127 and, in accordance with one embodiment, DEPI MCM Transmit Logic 200 a. That is, and as will be explained more fully below, DEPI MCM Transmit Logic 200 a in the UEQAM 150 encodes multiple channels of MPEG transport streams over a DEPI connection between the UEQAM and DS-PHY Module 155. The DEPI MCM Receive Logic 200 b in the DS-PHY Module is configured to demultiplex or decode the DOCSIS frames and deliver the resulting frames to respective stream processing resources such that the data encoded in the frames can be delivered to respective QAMs 180. DS-PHY Module 155 also includes an appropriate processor 125 and memory 127, which may include software instructions to perform the functionality of DEPI MCM Receive Logic 200 b.

More specifically, DEPI MCM Transmit Logic 200 a and DEPI MCM Receive Logic 200 b may be implemented as one or more hardware components, one or more software components (written in, e.g., C++, Java, microcode, among many other possible languages/implementations), or combinations thereof. That is, Logic 200 a and 200 b may be comprised of or be in communication with a programmable processor (microprocessor or microcontroller) or a fixed-logic processor 125. In the case of a programmable processor, any associated memory 127 may be of any type of tangible processor readable memory (e.g., random access, read-only, etc.) that is encoded with or stores instructions that may be employed to effect the DEPI MCM functionality described in more detail below. Alternatively, Logic 200 a and 200 b may be comprised of a fixed-logic processing device, such as an application specific integrated circuit (ASIC) or digital signal processor that is configured with firmware comprised of instructions or logic that cause the processor 125 or other component to perform the functions described herein. Thus, Logic 200 a and 200 b may take any of a variety of forms, so as to be encoded in one or more tangible media for execution, such as with fixed logic or programmable logic (e.g., software/computer instructions executed by a processor) and any processor may be a programmable processor, programmable digital logic (e.g., field programmable gate array) or an ASIC that comprises fixed digital logic, or a combination thereof. In general, any process logic may be embodied in a processor readable medium that is encoded with instructions for execution by a processor that, when executed by the processor, are operable to cause the processor or Line Card 122 to perform the functions described herein.

As further shown in FIG. 1, multiple QAMs 180 are provided to receive data processed in the DS-PHY Module 155 and thus deliver modulated data to respective cable modems 190 attached to the QAMs 180. As will be explained later herein with respect to FIGS. 8-11, a QAM might also deliver (in the form of an RF signal) MPEG encoded video that originated from, e.g., a video server, to a set-top-box that is configured to deliver a video signal to a connected television set.

The MCM connection or MCM interface 170 between UEQAM 150 and DS-PHY Module 155 via a packet switched link is enabled by DEPI MCM. DEPI is an Internet Protocol (IP) tunnel that exists between the DOCSIS MAC 120 in a modular cable modem termination system (M-CMTS) core and the UEQAM 150. One of the functions of DEPI is to take either formatted DOCSIS frames or MPEG packets (carrying video or data) and transport them through an OSI model layer 2 or layer 3 network (e.g., network 135) and deliver them to the UEQAM 150 for further transmission to DS-PHY Module 155 and for further transmission to the cable modems 190.

The base protocol that is used for DEPI is Layer 2 Tunneling Protocol Version 3, or “L2TPv3” (as defined in RFC 3931). L2TPv3 is an Internet Engineering Task Force (IETF) protocol that is a generic protocol for creating a “pseudowire,” where a pseudowire is a mechanism to transparently transport a layer 2 protocol over a layer 3 network. Examples of protocols supported by L2TPv3 include asynchronous transfer mode (ATM), High-level Data Link Control (HDLC), Ethernet, Frame Relay, Point-to-Point Protocol (PPP) over Ethernet, among others.

FIG. 4 (described in more detail later herein) depicts an L2TPv3 Transport Packet format that supports multiplexed DOCSIS frames. As will be explained, each data packet or frame contains, among other things, an expanded sub-layer header that enables a single, e.g., Ethernet Frame to carry packets from multiple MPEG channels and further enables the DS-PHY Module 155 to thereafter parse or demultiplex the packets and recreate the multiple channels that have been encoded and transmitted from the UEQAM 150.

Reference is now made to FIGS. 2A and 2B, which depict an example block diagram of a Line Card 156 in UEQAM 150 and the DS-PHY Module 155, along with data flowing into and out of those components. As shown, Line Card 156 is configured to receive multiple channels comprised of MPEG transport stream (TS) packets. Channels 0-N are depicted in the figure. Each of these channels is supplied at a predetermined MAS_(RATE) (modulation-annex-symbol rate) that is the constant bits-per-second derived from the fixed QAM Modulation, Annex Level and Symbol rate of the system. As further shown, each of the channels is then processed to be compliant with, e.g., a fixed ITU-T J.83 Annex, QAM and symbol rate. The processed individual channel data is then passed to the interface packet scheduler & DEPI encapsulation module 220. This module may be effectively controlled by DEPI MCM Transmit Logic 200 a in UEQAM 150. In a particular implementation, the MCM interface 170 between the Line Card 156 and DS-PHY Module 150 is via Ethernet (e.g., 10 GE, 40 GE or 100 GE).

On the other side of the interface between UEQAM 150 and its Line Card 156 and DS-PHY Module 155, DS-PHY Module 155 includes receive packet buffer and DEPI MCM de-encapsulation module 221, which receives, e.g., Ethernet frames via MCM interface 170, and de-encapsulates, parses or de-multiplexes the several MPEG-TS channels that have been transmitted via the DEPI pseudowire. As further shown, the de-encapsulated data streams are passed to respective packet processing modules to generate a data stream that has the same MAS_(RATE) as the original MAS_(RATE) at which the channel data was initially delivered to the Line Card 156. As will be seen in FIG. 3, the resulting channelized data streams are passed to respective QAM Processing Resources 355 and then QAMs for modulation.

In addition to the individual data channels 0-N that are passed between the Line Card 156 and DS-PHY Module 155, In-Band control messages may also be sent via, e.g., User Datagram Protocol (UDP) via In-Band control plane transmit module 123, which passes, for example, posted write and non-posted read requests to interface packet scheduler & DEPI encapsulation module 220 for transmission to DS-PHY Module 155.

Likewise, DS-PHY Module 155 includes a corresponding In-Band control plane receive module 124 that receives de-encapsulated control messages and (although not shown) passes any such messages for further processing.

To establish a complete two-way communication regime, DS-PHY Module 155 may also include a PHY Module to Line Card transmit interface and UDP encapsulation module 250 that enables the DS-PHY Module 155 to send information upstream towards Line Card 156 in UEQAM 150. In one possible embodiment, monitoring data (e.g., QAM monitoring data) can be streamed upstream to the Line Card 156. Also, In-Band UDP control messages can be transmitted to the Line Card 156 with such a configuration.

To receive any such DS-PHY Module-to-UEQAM data, Line Card 156 may include DS-PHY Module to Line Card Receive interface and UDP de-encapsulation module 251. Thus, with a configuration as shown in FIGS. 2A and 2B, multi-channel MPEG transport streams (which may be carrying DOCSIS compliant data) are transported from a Line Card associated with a UEQAM and transmitted to a DS-PHY Module 155 so that the data can be passed to QAMs 180 for delivery to cable modems 190 within end user premises.

FIG. 3 is an example block diagram of features of the DS-PHY Module 155, including QAM processing aspects thereof. On the left hand side of the figure is an interface and power module 310 that supplies digital input/output and power to the DS-PHY Module 155. Elements 312 represent the Ethernet MAC interfaces via which data is received from UEQAM 150. As shown, there may be multiple such Ethernet connections for a given DS-PHY 155. The next element or component in the block diagram is an Internet Protocol (IP) to stream processing resources (SPR) module 315. This module is responsible for parsing the individual channels received via the DEPI MCM protocol (carried via, e.g., Ethernet frames). Element 315 may be operated in accordance with DEPI MCM Receive Logic 200 b (not shown in FIG. 3). Each demultiplexed channel is then passed for further processing (as also shown in FIG. 2B). Specifically, the resulting MPEG TS (i.e., each MPTS) is supplied to a per-channel buffer 320 and then passed, depending on the type of data being carried by that MPEG TS, to either a DOCSIS Timestamp Replacement module 335, or to a video path module 340. Thereafter, the data stream is passed to a J.83 channel coding module 345.

Then, each respective processed channel is passed to SPR to QAM Mapping module 350, which is a part of QAM Processing Resources (QPRs). This module maps each channel to a selected QAM 180, wherein channel stacking and upconverting is effected in module 355, and where analog RF is produced in module 360 based on the data stream. The analog RF may then be transmitted via, e.g., a coaxial cable towards customer premises and their respective cable modems 190 (or set-top-boxes).

FIG. 4 shows a DEPI MCM data-plane Ethernet packet 405 format in accordance with one possible implementation. It is this packet format and information transmitted therein, and particularly the MCM sub-layer header and payload shown in FIG. 5, that enables multi-channel MPEG DEPI. First with reference to FIG. 4, there is shown a transport packet format used for encapsulating and transporting DOCSIS frames (or MPEG encoded video) over the MCM interface 170 between UEQAM 150 and DS-PHY Module 155.

Still referring to FIG. 4, an Ethernet header 410 is defined by IEEE-802.3. The Ethernet destination address (DA) of the Ethernet packet 405 is the Ethernet address of the destination (DS-PHY Module 155) or, perhaps, of the next hop router in a packet switched network assuming the UEQAM and DS-PHY Module were located distant from each other.

The Ethernet source address (SA) is the Ethernet address of, e.g., the UEQAM or its Line Card.

An Ethernet 802.1Q header 420 is defined by IEEE-802.1Q. Header 420 is optional and provides frame prioritization and Virtual Local Area Network (VLAN) support at layer 2 of the Open System Interconnect (OSI) model.

An IP header 430 is defined by RFC-791. An IP source address in header 430 is the IP address of the UEQAM 150 or its Line Card 156. The IP destination address is the IP address of the DS-PHY Module 155. The IP destination address may be an IP unicast or IP multicast address. Although element 430 is depicted in connection with IPv4, those skilled in the art will appreciate that other versions, such as IPv6 or like protocol may be employed.

The next portion of the Ethernet frame is L2TPv3 data header 440 that comprises a session identifier (ID), which designates a given session between two endpoints in the L2TPv3 tunneling protocol. Elements 450 and 460, L2TPv3 Sub-Layer header and the L2TPv3 payload, respectively, are discussed in detail with respect to FIG. 5. Finally a CRC code 470 completes the Ethernet packet 405.

FIG. 5 provides details with respect to the MCM Sub-Layer header and payload that is part of the DEPI MCM data-plane packet, and which provides the specific references to the individual channels being transmitted via the Ethernet frame 405 from UEQAM 150. The Sub-Layer header may be generated in the interface packet scheduler & DEPI encapsulation module 220, as controlled by DEPI MCM Transmit Logic 200 b.

Specifically, the L2TPv3 DEPI MCM Sub-Layer header 450 comprises multiple fields as follows:

V (1 bit)—VCC bit. This is set to zero and is reserved for compatibility with DEPI and VCCV.

S (1 bit)—Sequence bit. This bit is set to one to indicate that the sequence number field is valid. It is set to zero to indicate that the sequence field is not valid.

H (2 bits)—Extended Header bit. This set of bits is set to zero, which is the same value as in single channel DEPI. The In-Band Ethernet Control Plane chooses MCM Sub-Layer to indicate an MCM sub-layer header is being used to move multiple channels of MPEG in the same IP frame.

Flow ID (3 bits)—Identifies a flow.

Reserved—reserved for future use.

Packet count—indicates the number of individual packets being transmitted.

Sequence Number (2 bytes)—the sequence number increments by one each IP frame sent, and may be used by the receiver (e.g., DS-PHY Module 155) to detect packet loss. The initial value of the sequence number may be random, and thus unpredictable. The sequence number can be used to track lost IP frames.

MPTS Tag (1 byte)—The Multiple Program Transport Stream tag provides a pointer to a selected MPEG-TS Stream processing resource (FIG. 3: 320, 335/340, 345). The MCM IP frame carries multiple MPEG-TS packets all directed at different MPEG-TS processing engines and QAM channels.

MPTS Sequence Number (4 bits)—provides per-channel tracking information for the DS-PHY Module 155. The DS-PHY Module 155 receives MPTS tags and MPTS sequence numbers enabling the DS-PHY Module 155 to count per channel the MPEG-TS packets as they enter the DS-PHY Module 155. As such, the DS-PHY Module 155 may have the capability to replace per-channel MPEG-TS packets with MPEG NULL packets.

The payload 460 of the Ethernet frame includes the same number of MPEG-TS packets as there are MPTS tags in the Sub-Layer header 450, i.e., one tag per packet in the payload, thus enabling the processing of MPEG-TS packets from any one of the channels present at the Line Card 122. Up to 9 MPEG-TS packets per DEPI frame are permitted to keep the Ethernet frame payload below 2000 bytes.

Thus, those skilled in the art will appreciate that the L2TPv3 MCM Sub-Layer Header 450 and payload 460 described herein enables DEPI to carry multiple channels in the same Ethernet Frame. The combination of the L2TPv3 Sub-Layer Sequence Number and MPTS Sequence Number provide highly-reliable/100% error-recovery. Error recovery is defined as recovery of lost IP-Frames or lost MPEG-TS Payloads.

The error recovery can be performed at two levels: entire IP-Frame and MPEG-TS packet payload. The L2TPv3 Sequence Number may be helpful for tracking possible lost and/or out-of-order IP-Frames. The destination network component DS-PHY Module can use the L2TPv3 Sub-Layer Sequence number to identify the lost IP-Frame and correct the data-path with null IP-Packet insertion. The MPTS Sequence Number may also help to dynamically correct missing/lost channel-specific MPEG-TS packets. The destination network component DS-PHY Module can use the L2TPv3 Sub-Layer MPTS Sequence Number to identify the lost MPEG-TS Packets and correct the data-path with MPEG NULL Packets.

Further, those skilled in the art will appreciate that, whereas in a “single channel” DEPI implementation wherein all MPEG packets carried by a given IP Frame are meant for or fixed with respect to a single selected QAM, DEPI MCM permits a given IP Frame to carry MPEG-TS packets that may be destined for multiple respective QAMs. By allowing multiple channels within one session, protocol and product scaling may be more easily achieved. For example, a 10 GE link has enough bandwidth for 240 QAM channels. In accordance with the approach described herein, potentially all 240 QAM channels could be placed into a single DEPI MCM session (i.e., there would be 240 unique MPTS tags).

Further, single channel DEPI typically buffers seven MPEG-TS packets before encapsulating and forwarding them to the downstream DS-PHY 155. Such packets typically accumulate at a rate of 38 Mb/s. This represents a latency of about 0.5 ms. Since DEPI MCM can multiplex channels, only one MPEG-TS packet from each of seven (or 10) MPEG channels need be available before an IP Frame can be formed and sent. Accordingly, the approach described herein can reduce latency by up to about 86%.

FIG. 6 depicts a flowchart illustrating operations for effecting multi-channel MPEG DEPI between a first network element such as a UEQAM and a second network element such as a DS-PHY Module in a transmit direction in accordance with one possible implementation. At 610, multiple channels of, e.g., MPEG-TS packets are received in parallel at, e.g., a line card associated with a UEQAM. At 612, the line card (in conjunction with, e.g., DEPI MCM Logic 200 a) forms a packet switched communication frame including a sub-layer header. In this case, an Ethernet frame may be formed. At 614, MPEG-TS packets from multiple channels are encapsulated into a payload field of the communication frame. To identify each per-channel packet, and at 616, the sub-layer header is completed to include a tag associated with each channel. This tag may be used at the DS-PHY Module to select a specific stream processing resource to be employed to process the respective packets in the payload. At 618, the communication frame is transmitted towards the DS-PHY Module via, e.g., a packet switched network or direct connection.

FIG. 7 depicts a flowchart illustrating operations for receiving and de-multiplexing a multi-channel MPEG DEPI compliant frame received at a DS-PHY Module in accordance with one possible implementation. At 710, a communication frame is received including a payload and a sub-layer header. At 712, the frame is parsed to recover the individual per-channel packets from the payload. At 714, a stream processing resource is selected based on tag numbers respectively associated with individual ones of the packets in the payload. At 716, the individual packets are processed using the designated stream processing resources, and at 718, the data resulting from the processing is passed to, e.g., selected QAMs for upconverting and transmission to cable modems at customer premises.

In the embodiments described herein, the DOCSIS frames keep their DOCSIS Program Identifier (PID). Multiplexing is achieved by using a separate MCM table that uses a DEPI assigned identifier. This MCM table is what is stored in the DEPI packet header, i.e., the DEPI MCM Sub-Layer Header 450, as shown in FIG. 5. It is noted further that the intra-QAM channel multiplexing of streams of video and/or DOCSIS packets is performed before the packet-stream reaches the MCM interface 170. The MCM interface 170 moves individual QAM channel data that have already been bit-rate-shaped to meet the very perfect transmission bit-rates of DOCSIS and Video in the ITU-T J.83 digital data transmission standard. Further, DEPI MCM provides multiplexing per packet.

From the foregoing, those skilled in the art will appreciate that the DEPI MCM approach described herein enables packets from multiple channels of data being supplied at a UEQAM to be transmitted to a DS-PHY Module in a multiplexed fashion. This is in contrast to single channel DEPI which enables a single channel of an MPEG TS (which may carry DOCSIS frames) to be transported via, e.g., an Ethernet frame to a connected DS-PHY Module for further processing. By enhancing the L2TPv3 DEPI Sub-Layer header with a table comprising identification tags for each packet that is contained in the payload section of the frame, packets from multiple MPEG TS channels can be transported simultaneously in a single Ethernet Frame. The payload is then parsed within the DS-PHY Module and the respective streams are reconstituted to be identical to the original channel streams.

As explained, by implementing DEPI MCM it is possible to separate some of the functionality of a UEQAM and implement that functionality in a separate DS-PHY module. In some implementations, the distance over which the DEPI MCM connection 170 is made may be relatively small. And, in fact, in some implementations, even though DEPI MCM may be in operation, the UEQAM and DS-PHY may be co-located. That is, an MPEG multiplexer within the UEQAM employed to generate multiple program transport streams (MPTSs) is physically very close to the QAM in the DS-PHY Module that ultimately converts the digital stream into an RF stream. When a fiber node is employed downstream from the UEQAM, the MPTSs may then be sent to an analog optical transmission system for delivery to that fiber node over analog fiber. At the fiber node, they are converted to RF and delivered to a customer over coax cable. This analog optical transmission, however, can be expensive.

To avoid at least some of the analog optical transmission expense, and consistent with embodiments described herein, the MPEG multiplexer is maintained in the headend or UEQAM and the DS-PHY can be moved to the fiber node. However, there is a problem with such an architecture, particularly when the distance between the UEQAM and DS-PHY becomes relatively large, wherein the DEPI MCM connection becomes more susceptible to jitter. To address this jitter issue, MCL, or Multi Channel Launch, can be implemented along with DEPI MCM to enable longer distances, using an optical digital connection, between the UEQAM and the DS-PHY Module, which may be located in the fiber node. Succinctly, MCL, in accordance with embodiments described herein, allows an MPEG multiplexer to be connected to a DS-PHY Module over a long, asynchronous and high-jitter digital connection.

Reference is now made to FIG. 8, which is similar to FIG. 1, but is focused specifically on delivering video to a television set (or like monitor) that is connected downstream in a cable plant. Specifically, a video server 810 may obtain video (and related audio) content, from wide area network 130 and deliver that content to a UEQAM 150 that supports headend/CMTS functionality. (It should be noted that UEQAM 150 could also be disposed on the other side of CIN 135 and be co-located with, e.g., a CMTS.) As before in connection with the description of FIG. 1, the UEQAM 150 includes a processor 125 and memory 127, and further includes DEPI MCM/MCL Logic transmit 800 a. Also shown, in communication with processor 125, memory 127 and Logic 800 a is a primary MPEG multiplexer 820, the function of which is to receive multiple single program transport streams (SPTSs) and generate a rate-shaped multiple program transport stream (MPTS) by employing, e.g., the architecture shown in FIG. 2A. Under co-location circumstances, the MPTS would be delivered to a QAM for transmission. However, when not co-located, an extension to DEPI MCM, namely MCL, is provided to overcome asynchronous network and jitter issues.

An MCM/MCL connection 870 is provided between the UEQAM 150 and DS-PHY Module 155, which, as indicated in the figure, may be located in a fiber node. Connection 870 is similar to connection 170 (shown in FIG. 1), but connection 870 may be a much longer distance, e.g., on the order of kilometers, over which jitter might become a problem. The DS-PHY Module 155 includes a processor 125 and memory 127 as discussed earlier herein, and further includes DEPI MCM/MCL Logic receive 800 b. Also shown, in communication with processor 125, memory 127 and Logic 800 b is a secondary MPEG multiplexer 825, the function of which is to receive the MPTS from primary MPEG multiplexer 820 and, with timing information provided via MCL, provide a given MPTS to QAM 180 with appropriate timing. The QAM 180, in turn, converts the received MPEG MPTS digital stream into an RF signal, which is then supplied to a set-top-box 840 that is in communication with, e.g., a television 850.

It should be noted that Logic 800 a and 800 b (which provides MCL functionality) includes Logic 200 a and 200 b (MCM functionality) depicted in FIG. 1.

In one possible implementation, the secondary MPEG multiplexer 825 is implemented in hardware and includes a buffer that is smaller in size than a buffer provided for the primary MPEG multiplexer 820. MCM/MCL Logic 800 a is configured to control the primary MPEG multiplexer 820 to communicate pertinent details of the MPEG flow to the secondary MPEG multiplexer 825. These details (depicted in FIG. 9) include a per-packet launch number, which instructs the secondary MPEG multiplexer 825 regarding the ideal time to send a given packet to a QAM 180. The output of the primary MPEG multiplexer 820 is controlled such that its MPTS output is rate shaped to slightly less than the DS-PHY bandwidth available. The secondary MPEG multiplexer 825, as controlled by Logic 800 b, corrects for this mismatch by inserting Null packets as needed.

FIGS. 9A and 9B together show an MCM/MCL Sub-Layer header and payload that is part of the DEPI MCM/MCL data-plane packet in accordance with one possible implementation. This Sub-Layer header is similar to that shown in FIG. 5, but includes additional information that enables the secondary MPEG multiplexer, under control of Logic 800 b, to release received MPTS packets or Null packets at the appropriate time. Reference numeral 950 represents the L2TPv3 DEPI-MCM Sub-Layer header potion that was described above in connection with reference numeral 450 of FIG. 5, and need not be repeated here. Likewise the MPEG-TS packets themselves, identified by reference numeral 960, are the same as the payload 460 also described above with reference to FIG. 5.

Reference numeral 952 indicates the location in the L2TPv3 DEPI-MCM/MCL Sub-Layer header of the per-packet MPTS launch number. The MPTS launch number, in one possible implementation, is a 16 bit MPEG-TS packet launch code. The value of the launch code tells the secondary MPEG multiplexer 825/Logic 800 b when to launch the data packet. The MPTS launch number runs, in one possible implementation, off of a 45 KHz clock, where the 45 KHz clock may be synchronous and divided down from, e.g., a system video 27 MHz clock.

Reference number 954 is still another element provided by MCL that enables a longer connection between the headend and a fiber node over a digital optical medium. Element 954 provides Program Clock Reference (PCR) correction to enable PCR re-stamping at the output of the secondary MPEG multiplexer 825. In an implementation, a PCR Base is a 33 bit value consistent with ITU-T H.222.0. The PCR Base offset is the offset between the local line card source PCR clock, e.g., the primary MPEG multiplexer and the network destination source PCR clock, e.g., the secondary MPEG multiplexer.

A PCR-extension offset of 9 bits is also provided and can be used to complement the PCR base offset value. The bit identified as “P” is a 1 bit flag to indicate whether the PCR data is to be used or not.

FIGS. 10 and 11 depict example flowcharts illustrating operations for effecting MPEG MCL between the primary MPEG multiplexer and the secondary MPEG multiplexer in accordance with one possible implementation. FIG. 10 depicts a flowchart illustrating operations for effecting multi-channel MPEG DEPI-MCL between a first network element such as a UEQAM and a second network element such as a DS-PHY Module deployed in, e.g., a fiber node, in a transmit direction in accordance with one possible implementation. At 1010, multiple channels of, e.g., MPEG-TS packets are received in parallel at, e.g., a line card associated with a UEQAM. At 1012, the line card (in conjunction with, e.g., DEPI MCL Logic 800 a) forms a packet switched communication frame including a sub-layer header. In this case, an Ethernet frame may be formed. At 1014, MPEG-TS packets from multiple channels are encapsulated into a payload field of the communication frame. To identify each per-channel packet, and at 1016, the sub-layer header is completed to include a tag associated with each channel. This tag may be used at the DS-PHY Module to select a specific stream processing resource to be employed to process the respective packets in the payload. In addition, at 1018, a per-packet launch number is added to the sub-layer header for respective packets. The launch number designates when, e.g., the secondary MPEG multiplexer should release the packet to a QAM. At 1020, the communication frame is transmitted towards the DS-PHY Module via, e.g., a packet switched network or direct connection. In addition to the launch number associated with packets in the payload, the methodology may also include providing a per-packet PCR correction or offset value that may be used in connection with re-stamping PCR values in MPEG packets being released from, e.g., the secondary MPEG multiplexer 825.

FIG. 11 depicts a flowchart illustrating operations for receiving and de-multiplexing a multi-channel MPEG DEPI compliant frame received at a DS-PHY Module and timely launching de-multiplexed packets towards a QAM for transmission to, e.g., a set-top-box, in accordance with one possible implementation. At 1110, a communication frame is received including a payload and a sub-layer header. At 1112, the frame is parsed to recover the individual per-channel packets from the payload. At 1114, a stream processing resource is selected based on tag numbers respectively associated with individual ones of the packets in the payload. At 1116, the individual packets are processed using the designated stream processing resources. At 1118, the specific launch time of individual packets is determined from information provided in the sub-layer header. At 1120, the data resulting from the processing is passed or released to, e.g., a selected QAM for upconverting and transmission to cable modems at customer premises. PCR re-stamping may also be performed in view of PCR correction or offset data provided in the sub-layer header on, e.g., a per-packet basis.

Although the embodiments described herein may have particular applicability in a modular CMTS environment where components are physically distributed in a network, the MCM and MCM/MCL functionality can also be employed in connection with an integrated CMTS (I-CMTS) environment. That is, although components of an I-CMTS may be more closely physically bundled, the functionality described here may nevertheless be helpful to enable the multiplexing of multiple channels of MPEG transport streams.

Although the system and method are illustrated and described herein as embodied in one or more specific examples, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the scope of the apparatus, system, and method and within the scope and range of equivalents of the claims. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the apparatus, system, and method, as set forth in the following. 

What is claimed is:
 1. A method comprising: receiving, at a first network element, multiple channels of video delivered as respective streams of packets; forming a packet switched communication frame including a sub-layer header; encapsulating packets from the multiple channels of video into a payload field of the packet switched communication frame to obtain encapsulated packets; identifying the encapsulated packets in the payload field with respective tags in the sub-layer header; designating the encapsulated packets in the payload field with respective launch values in the sub-layer header; transmitting the packet switched communication frame to a second network element, determining respective times for passing the packets from the multiple channels of video to at least one quadrature amplitude modulator (QAM) based on the respective launch values of the packets in the sub-layer header; and passing, at the second network element, the packets from the multiple channels of video to the at least one QAM at the respective times for passing.
 2. The method of claim 1, wherein the first network element comprises a universal edge quadrature amplitude modulator (UEQAM).
 3. The method of claim 1, wherein the streams of packets are compliant with a Motion Picture Experts Group (MPEG) transport streams (TS).
 4. The method of claim 1, wherein the packet switched communication frame comprises an Ethernet Frame.
 5. The method of claim 1, wherein the sub-layer header is in conformance with a Layer 2 Tunneling Protocol version 3 (L2TPv3) sub-layer header.
 6. The method of claim 1, further comprising adding Program Clock Reference (PCR) offset data to the sub-layer header on a per-packet basis.
 7. The method of claim 1, further comprising calculating the launch value using a 45 MHz clock derived from a 72 MHz video system clock.
 8. An apparatus, comprising: a multiplexer; and a processor configured to: receive multiple channels of video delivered as respective streams of packets and multiplex the same in the multiplexer; form a packet switched communication frame including a sub-layer header; encapsulate respective packets from the multiple channels into a payload field of the packet switched communication frame to obtain encapsulated packets; identify the encapsulated packets in the payload field with respective tags in the sub-layer header; designate the encapsulated packets in the payload field with respective launch values in the sub-layer header; transmit the packet switched communication frame to a downstream network element; and determine respective times for passing the packets from the multiple channels of video to at least one quadrature amplitude modulator (QAM) based on the respective launch values of the packets in the sub-layer header, wherein, at the downstream network element, the packets from the multiple channels of video are passed to the at least one QAM at the respective times for passing.
 9. The apparatus of claim 8, wherein the apparatus is configured to operate as a universal edge quadrature amplitude modulator.
 10. The apparatus of claim 8, wherein the processor is further configured to identify the encapsulated packets in the payload field with a sequence number.
 11. The apparatus of claim 8, wherein the processor is further configured to add a per packet Program Clock Reference (PCR) offset value to the sub-layer header.
 12. The apparatus of claim 8, wherein the processor is further configured to calculate the launch value based on a 45 KHz clock derived from a 72 MHz video system clock.
 13. A method comprising: receiving, from a universal edge quadrature amplitude modulator (UEQAM), a communication frame including a payload and a sub-layer header; recovering video packets from the payload of the communication frame; selecting stream processing resources based on information in respective tags in the sub-layer header, wherein the tags correspond with respective video packets; processing the video packets using the selected stream processing resources; determining a time for passing respective video packets to at least one quadrature amplitude modulator (QAM) based on launch values received on a per-packet basis in the sub-layer header, and passing the respective video packets to the at least one QAM at respective times for passing.
 14. The method of claim 13, further comprising re-stamping Program Clock Reference (PCR) data in respective video packets based on PCR offset data provided in the sub-layer header.
 15. The method of claim 13, wherein the communication frame comprises an Ethernet frame and the sub-layer header in conformance with a Layer 2 Tunneling Protocol Version 3 (L2TPv3) sub-layer header.
 16. The method of claim 13, wherein the video packets are compliant with a Motion Picture Experts Group (MPEG) standard.
 17. An apparatus comprising: a processor; and a memory; the processor configured, based on instructions in the memory, to: receive, from a universal edge quadrature amplitude modulator (UEQAM), a communication frame; recover video packets from the payload of the communication frame; select stream processing resources based on information in respective tags in a sub-layer header, wherein the tags correspond with respective video packets; process the video packets using the selected stream processing resources; determine a time for passing respective video packets to at least one quadrature amplitude modulator (QAM) based on launch values received on a per-packet basis in the sub-layer header, and pass the respective video packets to the at least one QAM at respective times for passing.
 18. The apparatus of claim 17, wherein the processor is further configured to re-stamp Program Clock Reference (PCR) data in respective video packets based on PCR offset data provided in the sub-layer header. 